High-grade contaminationless plasma burner as light source for spectroscopy



April 21, 1970 l.. vEcsl-:RNYES 3,508,106

HIGH-GRADE CONTAMINATIONLESS PLASMA BURNER AS LIGHT SOURCE FOR SPECTROSCOPY Filed April 14, 1967 Inf. c1. no1-i 7/24, 3/00 U.S. Cl. 313-231 3 Claims ABSTRACT oFTHE DISCLOSURE A direct current plasma jet having a cathode adapted to guide the arc and plasma and being removably mounted in a block, said cathode and block being lat least partly surrounded by a bellghaving a plasma outlet laligned with the outlet of said cathode. Said bell is formed with a further aperture through which a sample guide' tube protrudes. A protective ring is arranged around the cathode within the bell.

The invention relates to a plasma jet, particularly a vertical plasma jet forgspectroscopic purposes, generating plasma by means of a direct current arc.

The plasma jet according to the invention comprises a feeder head including a jcathode, adapted toguide the arc and plasma and fastened removably in a block, the block and the cathode being at least partly surrounded by a bell having a plasmal outlet aligned with an outlet of the cathode, a sample guide tube protruding` through a side wall of the bell fromoutside to the interior of the bell, a protective ring being arranged around the cathode inside the bell. .A

An anode may be in the lform of a disc provided with openings. The inlets of the openings may be arranged in a circle and their outlets in another circle, the circles being parallel and co-axial with axis of the anode, axes of the openings being skew lines inclined at a same angle to the axis ofthe anode.. f l 1 By the foregoing arrangement, a compact, readily manufactured vertical plasma jet suitable foi* spectroscopic purposes is provided. The plasma jet accgding to the invention provides a substantially higher eiciency than the prior art arrangements. Further, only Va viminimum number of parts 'need be replaced or cleaned between samples to avoid the problems of contamination or memoryf For a fuller understanding of the invention, reference is had to the following description taken in connection with the accompanying drawing, in which:

The sole figure is a section of the vertical plasma jet according to the invention. 'f 'f The illustrated vertical plasma iet comprises a` feeder head comprising a vertically extending tube cathode 13 the lower end of which is tapered and removably fastened in a vertical nub-like portion of a cathode block 19. The cathode 13 is surrounded by a cathode bell 18 provided with a plasma outlet 16, Aco-axial with the cathode 13. A sample inlet tube 17 protrudes through a side wall of the bell 18 to the interior of the bell. A protecting ring 20 is disposed around the cathode 13 and bears on the upper surface of the nub ofthe block 19 to prevent the block from becoming contaminated. When powder or liquid samples are used,the cathode 13 and ring 20 get contaminated and have to be replaced for every sample. The sample inlet tube 17 and the cathode 'bell 18 have to be replaced too, but, after having been cleaned they can be reuseda United States Patent O Patented Apr. 21, 1970 ICE The feeder head is surrounded by a water-cooled supporting disc 21 bearing on an insulating washer 22, disposed in an annular seat.

Water-cooled `stabilizer discs 14 and 15 defining an arc channel co-axial with the cathode 13 are arranged below the disc 2:1. An anode 12, carried by a water-cooled supporting disc "23, is disposed below the stabilizer discs 14 and 15. An insulating washer 24, disposed in an annular seat, is placed between the disc 14 and the disc 23'. The anode 12 is provided with a central, vertical opening plugged with a ,rounded pin 25 forming a replaceable portion of anode 12 and made ofthe same material as said anode. Said borings are adapted to introduce a plasma producing gas and to stabilize the arc. The arc is burned betweenf'ithe plug 25 and the top of the tubular cathode 13.

The inlets of the openings 34 are arranged in a circle and their outletsl are arranged in another circle of a smaller diameter both circles being parallel and co-axial with the axis oflfthe anode 12. The axis of the openings 34 are skew lines, all inclined at the same angle to the axis of the anode. An anode cell 26 disposed below the anode 12 is adapted to lter and uniformly supply the borings 34 withflfthe gas. A replaceable anode cell lfiller 27 and a gas inlet tube 29 are surrounded by a threaded pressure cap 28,'jvAnode cell 26 may also serve as a gas sample mixing chamber where gas samples are introduced together with working gas through gas inlet tube 29.

The stabilizer'jgliscs 14 and 15 are xed in position by a metal ring 31. 'libe burner jet assembly is heldto'gether by two insulated screws (not illustrated), preferably of an insulating material, extending through holes 32 and screwed into tapped holes 33.

The initiation of the plasma jet is performed by the insertion and rernoval of a graphite rod through the plasma outlet 16 I and the bore of the tubular cathode 13.

r The arc is formfved between plug 25 in anode 12 and the top of tubular cathode 13.

The gas, necessary for generating a plasma is introduced through the tube 29 as indicated by arrow 30.

The anode 12,V cathode 13, inlet tube 17, cathode bell 18, cathode block 19, protecting ring 20 and anode filler 25 are preferably made of spectrally pure graphite, the stabilizer discs 14 and 15, supporting discs 21 and 23, the pressure cap 28 fand the ring 31 are preferably made of copper, whereas the anode cell filler 27 and the gas inlet tube 29 are preferably made of a material known under the trade name Teon 1 If the arc voltage is 45 v., the plasma jet operates wi a power consumption of 2O to 40 amps, i.e. with a power 0.9 to 1.8 kw. and is able to produce a metallic contaminationless plasma beam of mm. overall length having a free useable core of 10 to 30 mm.

plasma jet can use any usual inert gas and consumes an average total of 5 to 10 litres per minute. On altering the size of the apparatus, an even wider range can be achieved.

What I claim isf:

1. A vertical plasma jet for the generation of plasma in a direct current arc comprising an anode, a cathode block formed with a central aperture therethrough; means for maintaining said cathode block aperture and said anode in spaced vertical relation; a tubular cathode removably mountable on said cathode block in alignment with said anode and cathode block aperture, said tubular cathode projecting from the side of said cathode block away from said anode; a bell disposed in spaced relation about the projecting portion of said cathode and engaging said cathode block, said bell having a plasma outlet opening therein aligned with the bore of said cathode and said bell having a side aperture therein; a sample guide extending through said bell side aperture to permit the insertion of samples into the space between said bell and cathode; and a protective ring member exposed about the projecting portion of said cathode and adapted to shield the portion of the surface of said cathode block extending between said cathode and said bell.l

2. A plasma jet as recited in claim 1, wherein said anode is formed as a disc having a plurality of spaced bores therethrough, the inlets of said bores being arranged in a first circle, the outlets of said bores being arranged in a second circle, said rst and second circles lying in parallel planes and being coaxial with the axis of said anode, the axes of said bores being skew lines inclined at a uniform angle to the axis of the anode, a plasma inducing gas being introduced through said bores.

3. A' plasma jet as recited in claim 2, including an anode cell about the inlet openings of said anode bores, said anode cell being formed with an aperture therethrough; and a gas inlet pipe extending through said anode cell aperture, said anode cell being adapted as a gas sample mixing chamber for mixing gaseous samples and said plasma producing gas, said mixture passing through said anode bores.

References Cited UNITED STATES PATENTS JAMES W. LAWRENCE, Primary Examiner P. C. DEMEO, Assistant Examiner U.S. C1.7 X.R.. 219,-121; 356-85 

